I came across this device from the OpenWRT trunk list recently, it runs on Atheros 933x@400Mhz with 4/32MB Flash/RAM size, the switch chip seem vlan capable.
It was selling at about RM50 something only, really not bad with such a spec 
, so I just bought 1 to test on OpenWRT trunk build ....
Company: TP-Link
Product: http://www.tp-link.com/en/products/details/?model=TL-WR740N
FCC ID : TE7WR741NDV4
Stock Firmware/Utilities/Manual : http://www.tp-link.com/en/support/download/?model=TL-MR3420&version=V1#tbl_j
OpenWRT : http://wiki.openwrt.org/toh/tp-link/tl-wr740n
Firmware (trunk) : http://downloads.openwrt.org/snapshots/trunk/ar71xx/ (use "xxx-tl-wr740n-v4-xxxx")
Factory to OpenWRT :Via webgui, use "xxx-factory-xxx.bin"
Revert to Factory : Via FailSafe mode (QSS button), use stock firmware file with "xxx-up-xxx.bin"
Confirmed FailSafe mode through QSS button works on Trunk R30919 while I was testing the UniFi
19Mar2012 : Managed to get internet vlan.500 PPPoE works ok, still unable to get IPTV vlan.600 working ........ 
Click the following for :
Flash to OpenWRT (Trunk version) & Install LuCI Webgui